The invention relates to the fixing of semiconductor modules, in particular power semiconductor modules, e.g. IGBT modules, to a heat sink. Power semiconductor modules are technically constructed by soldering electronic components onto ceramic substrates that are usually (optionally) soldered onto a base plate that serves as a heat sink. In order to operate a power semiconductor module, the heat produced in the components must be reliably dissipated. Because the optional base plate is usually inadequate for that purpose, the semiconductor module is generally flanged onto a heat sink, or screwed to the latter, by the substrate or base plate at the side.
In order to ensure reliable heat transfer, during assembly thermally conductive paste or foil is usually introduced between the two contact areas, i.e. between the heat sink and the substrate or the base plate, in order to compensate for undulations and roughness. Because the connection looses strength upon heating, the contact thermal resistance increases. Strength is lost as a result of an increase in the amount of settling as a result of the reduced viscosity of the thermally conductive paste and/or foil, or, in the case of phase change materials, changes from the solid state to a soft (liquid) state. For this reason, after heating, retensioning of the screw joint or an additional arrangement of spring rings in the case of the screw joint is recommendable.
For this reason, the additional assembly outlay of a screw connection and, in the case of inexpensive components, the joint increases the assembly costs. These additional costs occur even without the additional outlay of retensioning that is required after operational start-up.
It is accordingly an object of the invention to provide a spring clip for fixing semiconductor modules to a heat sink that overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of the general type and that produces a cost-effective, simple and reliable connection between a semiconductor module and a heat sink.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a heat sink assembly for at least one semiconductor module. The heat sink assembly includes a heat sink formed with a spring clip receptacle. A spring clip holds a semiconductor module on the heat sink. The spring clip engages the spring clip receptacle.
With the objects of the invention in view, there is also provided a semiconductor module assembly for fixing to a heat sink. The semiconductor module is formed with a second spring clip receptacle. A spring clip holds the semiconductor module on a heat sink. The spring clip engages the semiconductor module.
The generic semiconductor module also can be fixed to a generic spring clip for fixing a heat sink that is not configured according to the invention.
The generic semiconductor module also can be configured according to the invention to a semiconductor module that is not configured according to the invention.
With the objects of the invention in view, there is also provided a spring clip for fixing a heat sink to a semiconductor module. The spring clip includes a side engaging a spring clip receptacle for automatic holding of a semiconductor module and a heat sink.
According to the invention, one or more clips made of spring material, i.e. spring clips, clamp the semiconductor module onto the heat sink. The heat sink may, as an extruded profile, already have the desired form that the heat sink requires to receive a clip without additional reworking of the heat sink being necessary. The connection is more favorable than a screw joint because assembly can be completed more simply and more rapidly. Furthermore, given a sufficient pretensioning distance, such a spring clip compensates for the amount of settling between heat sink and semiconductor module, so that a reliable heat transfer can be permanently ensured without retensioning or other assembly steps that are necessary after initial operation or during operation. The clips always ensure that the desired tensioning force is provided. The spring clips have a simple form and may be composed of an elastic material, preferably spring steel.
According to the invention, a mutually matched form of the clips and heat sinks or semiconductor modules advantageously optimizes the efficient fixing. In this case, the clip and heat sink or semiconductor module can be connected by inserting or latching into place the clip and automatically holding on/in the heat sink or semiconductor module. The connection can be made even when the spring clip is not in the tensioned state in which the semiconductor module is connected to the heat sink with the spring clip.
According to one embodiment variant of the invention, the heat sink or the semiconductor module has, for this purpose, a groove over the entire length or at least in the region of a spring clip receptacle in which the spring clip is fixed to the heat sink or semiconductor module. As an alternative, instead of a groove, the heat sink or the semiconductor module also may have a collar. The collar can hold a spring clip, which in turn can be latched into place.
Furthermore, according to a further advantageous embodiment, the spring clip is shaped in such a way that the semiconductor module or the heat sink, without additional lateral forces, latches into place itself solely by an assembly force acting in one direction. As a result, a simple fixing of a plurality of semiconductor modules on a heat sink or a plurality of heat sinks on a semiconductor module over the entire length can be produced.
According to another advantageous embodiment, the housing of the semiconductor module acquires, as early as in the casting process, a suitable basin for latching in the spring clip. The basin preferably has a curb. This does not additionally increase the costs. A spring clip then can be inserted automatically into the basin, e.g. before the printed circuit board is soldered above it because doing so would make the arrangement of the clip more difficult. Preferably, a semiconductor module acquires at least two basins provided on opposite sides. Furthermore, a plurality of spring clips can be inserted into a basin or, instead of a basin-shaped spring clip receptacle, a differently shaped receptacle may be provided, e.g. a step-shaped receptacle. After the semiconductor module has been placed onto the heat sink, the suitably shaped clips can be latched, with the aid of a tool, e.g. specially shaped tongs, with high reliability and accuracy, preferably in an automated manner, into grooves provided therefor in the heat sink. If the semiconductor module is already soldered to a circuit carrier, then this latching operation can be performed without difficulty only from the side. A spring clip matched to this embodiment preferably has three bending edges, and it rocks about the first bending edge during the latching operation, and a tensioning arc is produced about the second and third bending edges. The clamping can be effected at an optional fourth bending edge.
Other features that are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a spring clip fixing semiconductor modules to a heat sink, it is nevertheless not intended to be limited to the details shown, because various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.